1. Field of Invention
The invention relates to a method and apparatus for generating hydrogen gas in a controlled manner from the dissociation of water. The controlled nature of the method and apparatus allow the production of hydrogen on demand, making the apparatus and process suitable for producing hydrogen for a variety of uses.
2. Description of Related Art
Hydrogen gas can be produced by a number of known chemical reactions. For example, it is known that reacting metals with mineral acids can produce hydrogen and a metallic compound according to the reaction:Metal+Acid→Metal Compound+Hydrogen GasExamples of reactions using zinc and iron with hydrochloric and sulfuric acids are:Zn+2HCl→ZnCl2+H2↑Fe+H2SO4→FeSO4+H2↑
Potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), aluminum (Al), zinc (Zn), iron (Fe), and lead (Pb) are among those metals that will yield hydrogen gas when reacted with dilute mineral acids.
It is also known in the art that alkali metals and alkaline earth metals can react with water to form hydrogen and the corresponding alkali or alkaline earth hydroxide. This reaction, however, is typically rapid and intense, sometimes violent. It generates significant heat, and often the generated hydrogen explodes.
For example, sodium and calcium metals react violently with water to produce heat, release hydrogen and form the metal hydroxide:2Na+2H2O→H2÷2NaOH
Certain hydrides such as calcium hydride and sodium boro-hydride react with water to release hydrogen:CaH2+2H2O→Ca(OH)2+2H2↑NaBH4+4H2O→NaB(OH)4+4H2↑
It is also known that certain alkali metal hydroxides in aqueous solutions will react with metals to form intermediate compounds and release hydrogen gas. Sodium, potassium and lithium hydroxides, etc., will react with aluminum, zinc, silicon iron, lead, etc., to generate heat, release hydrogen gas and form intermediate compounds. In the literature, for example:2Al+2NaOH+6H2O→2NaAl(OH)4+3H2↑Si+4NaOH→Na4SiO4+2H2↑
Almost without exception these reactions are violent and are exothermic in nature, generating significant quantities of heat. The uncontrolled nature of the reactions can elevate the temperature to such a degree that the hydrogen gas generated can ignite, resulting in an explosion.
Numerous closed cycle, often multi-step processes which dissociate water into hydrogen or into hydrogen and oxygen are disclosed in U.S. Pat. Nos. 3,821,358; 3,928,549; 4,011,305, 3,969,495; 3,574,561, 4,182,748; 4,207,095; 4,287,169 and 4,289,744. Of particular interest to this invention are U.S. Pat. Nos. 5,817,157 and 5,782,464 (Checketts), and U.S. Pat. No. 5,690,902 (Werth). The Checketts patents call for a series of coated sodium pellets to be presented on demand to water in a reactor, the coating removed and the sodium allowed to react with the water to form hydrogen and the alkali hydroxide. In order for this scheme to generate sufficient hydrogen for any practical purpose, the sodium pellets would likely have to be of such size as to cause a rapid, intense reaction with the water, along with the generation of significant heat which would raise the temperature of the reaction to the point where spontaneous explosion of the generated hydrogen is possible. Though correct in theory, the Checketts patents fall short of practical application.
The Werth patent calls for the generation of hydrogen from the oxidation of iron particles by water in the presence of what is called a catalyst, potassium hydroxide, at elevated temperatures. In actuality an alkali hydroxide solution will react with the iron to form hydrogen, the alkali metal hydroxide and iron oxide. The potassium hydroxide is not, therefore, a catalyst but is involved in the chemical reaction. As iron oxide is formed on the surface of the iron particles, they become impervious to further action by either the hydroxide or the water, requiring a constant interchange of fresh iron particles, with the majority of the iron being unreacted. Though also correct in basic theory, the Werth patent also falls short of practical applicability.
In order to utilize any, or all, of the possible methods of producing hydrogen gas from the thermo-chemical dissociation of water, it is necessary to control the reaction so that specific volumes of hydrogen gas per unit of time at specific pressures can be delivered for practical utilization. The invention of this application relates to such a control methodology.